Adachiite is a rare member of the tourmaline group, chemically characterized by its calcium- and iron-rich composition. It typically presents as dark, prismatic crystals found in association with metamorphic assemblages in Japan, requiring professional analysis to distinguish from more common iron-rich tourmalines like schorl.
Is this adachiite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch adachiite with a known reference. Adachiite sits at Mohs 7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Adachiite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Adachiite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark green, dark brown, black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: prismatic crystals with rounded triangular cross-sections.
Often confused with
Adachiite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside adachiite
Minerals reported to co-occur with adachiite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe₃Al₆(Si₅AlO₁₈)(BO₃)₃(OH)₃(OH)
- Mohs hardness
- 7
- Density
- 3.31 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Prismatic Crystals with Rounded Triangular Cross-sections
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $50-300 per specimen
Where rockhounds find adachiite
Classic worldwide localities
- Adachi mine, Fukushima Prefecture, Japan
Field-hunting tip
Look in metamorphic rocks country, the host setting where adachiite typically forms. If you start seeing quartz, albite, muscovite in float, you are in the right ground. Field specimens usually show a prismatic crystals with rounded triangular cross-sections habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify adachiite?+
Where is adachiite found?+
How much is adachiite worth?+
What rocks look like adachiite?+
What minerals are found with adachiite?+
What kind of rock does adachiite form in?+
What is adachiite used for?+
Find adachiite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
